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Fertilization and normal embryonic and early fetal development
Published in Hung N. Winn, Frank A. Chervenak, Roberto Romero, Clinical Maternal-Fetal Medicine Online, 2021
Asim Kurjak, Ritsuko K. Pooh, Aida Salihagic-Kadic, Iva Lausin, Lara Spalldi-Barisic
A small intradecidual gestation sac can be seen by transvaginal sonography between 32 and 34 days (Figs. 11 and 12). The secondary yolk sac is the earliest extraembryonic structure normally seen within the gestational sac at the beginning of the 5th gestational week (Fig. 13). Yolk sac volume increases from week 5 to 10. When it reaches its maximum at week 10, it would have already started to degenerate, which can be seen by the significant reduction in visualization rates of the yolk sac vascularity. The start of embryo-chorionic circulation changes the source of nourishment to all intraembryonic tissues. Development of the embryo becomes dependent on the circulation of embryonic blood. In the embryo, there are three distinct blood vascular systems: vitelline circulation (from yolk sac to embryo), intraembryonic circulation, and feto-placental circulation. It is possible to visualize and assess them virtually from conception.
Embryology of veins and lymphatics
Published in Ken Myers, Paul Hannah, Marcus Cremonese, Lourens Bester, Phil Bekhor, Attilio Cavezzi, Marianne de Maeseneer, Greg Goodman, David Jenkins, Herman Lee, Adrian Lim, David Mitchell, Nick Morrison, Andrew Nicolaides, Hugo Partsch, Tony Penington, Neil Piller, Stefania Roberts, Greg Seeley, Paul Thibault, Steve Yelland, Manual of Venous and Lymphatic Diseases, 2017
Ken Myers, Paul Hannah, Marcus Cremonese, Lourens Bester, Phil Bekhor, Attilio Cavezzi, Marianne de Maeseneer, Greg Goodman, David Jenkins, Herman Lee, Adrian Lim, David Mitchell, Nick Morrison, Andrew Nicolaides, Hugo Partsch, Tony Penington, Neil Piller, Stefania Roberts, Greg Seeley, Paul Thibault, Steve Yelland
The yolk sac provides a blood supply and a source of nutrients during early development, but the vitelline circulation ceases by the fourth week as the yolk sac atrophies to be incorporated into the primordial gut.
Twin Fetus-in-Fetu: The Story of an Encaged Twin
Published in Fetal and Pediatric Pathology, 2023
Md Ali Osama, Priti Chatterjee, Amit Gupta
The theory of monozygotic diamniotic twins has been increasingly proposed recently [3,4]. In this “included-twin” theory, the parasitic twin is incorporated into the body of the host twin after anastomosis of the vitelline circulation [4]. Typing of blood group, karyotyping, DNA analysis and other genetic studies all showed identical findings between the parasitic fetuses and their hosts [5]. Although these findings are compatible with both monozygotic multiple pregnancy and the teratoma theory, the World Health Organization considers it to be the most well-differentiated end of teratoma. The true etiology still remains ambiguous. This condition is usually asymptomatic, or may present as a painless mass with or without associated pressure symptoms. It is most frequently located in retroperitoneal area; other areas include the sacro-coccygeal region, cranium, scrotum, pelvis, liver, and adrenal gland [6–8]. FIF must be differentiated from teratoma as a teratoma has a higher risk of malignant transformation.